Parasound amp and pre amp issue: repaired but not repaired

pglbookpglbook Posts: 1,518
edited February 9 in Electronics
I took my Parasound HCA 1500A amp and P/LD 1500 pre to get repaired 3 weeks ago. This morning I drove to Syracuse (2 1/2 hours away) in a snowstorm and picked them up. The pre amp had a power supply rebuild and a few other tweaks (a few caps or resistors changed as well) and the amp just had some servicing and cleaning and making sure everything in spec. I hooked everything up about an hour ago and there are still issues. Before there was no sound when I hooked everything up. Now there is sound but the sound of one speaker is noticeably lower in volume than the other speaker. I switched the speaker wires on the back of the amp and the problem has now gone to the other speaker (and the sound of the speaker whch initially had the problem is fine). Any thoughts on what it is? A bad channel in amp? Unbelievable!! $600 in repairs later and now I have to take everything back again to get fixed (again). Doesn't anyone know how to fix vintage equipment correctly anymore? I had heard good things about this tech but it seems like he did not get it right. Is there any risk to my equipment if I play the amp and pre amp like this until I can take the equipment back next weekend. It is the only system I currently have and I'd like to listen to some musc this week even if the sound is off on one speaker. Thanks.
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Comments

  • mhardy6647mhardy6647 Posts: 20,982
    edited February 9
    What are you using for a source?
    What did you do to establish that the offset in levels between channels wasn't from your source (including the cables involved)?

  • pglbookpglbook Posts: 1,518
    My set up is: Parasound HCA 1500A amp, P/LD 1500 pre, Rotel RCC 1055 CD player, Polk SDA 2B TL speakers, Thorens TD 160 tt. I had been playing a CD.
  • mhardy6647mhardy6647 Posts: 20,982
    edited February 9
    I'd suggest swapping the L and R cables from your CD player to the preamp input and see if the low level follows the input or not. It could even be one of the cables, since presumably you've unhooked and 're-hooked' them recently. Perhaps a poor connection at one end or the other of one of the cables.

    That, and/or swap which input on the preamp to which the CD player's connected (e.g., from "AUX" to "TUNER" or to one of the "TAPE PLAYBACK" inputs, and engage the tape monitor).

    Might have a dirty source selector switch or other control. Unless the 'tech' said the controls were cleaned, they may not have been.

  • pglbookpglbook Posts: 1,518
    edited February 9
    Thanks, mhardy. How would it be from cables? I did change my CD player RCA cables because I needed a longer cable to connect it to the pre. I bought a RCA cable (used, I guess) at the stereo repair shop this morning. My CD player has always played fine and, while waiting for the repair to my Parasound pre and amp, I had it hooked up to my Yamaha CR 2040 receiver and everything played fine.

  • mhardy6647mhardy6647 Posts: 20,982
    I updated my previous post -- could be a poor connection in one of the cables' terminations, or even just poor contact with the preamp input or the CDP output.

    It is certainly possible that there's a problem in your just-repaired preamp or power amp... but it's also very possible that your operations in removing or replacing them from the system have left something a little out of kilter. It should be straightforward to "rule in" or "rule out" the signal getting into the preamp as being the "root cause".

  • lightman1lightman1 Posts: 10,185
    Hardy is a hack.....
  • mhardy6647mhardy6647 Posts: 20,982
    If the problem isolates to (preamp + power amp) from the suggestions above, I'd suggest that, if possible, the next step would be to ISOLATE the preamp and power amp and see which were the culprit.

    IF (!!!) your CDP has a variable output level (either via its remote control or a 'volume' control on the player itself) you can connect it directly to the power amp input (i.e., bypass the preamp). TURN THE VOLUME WAY DOWN, of course, on the player, then gingerly adjust it up and see if the levels are (still) unbalanced. If not, the problem could be in the preamp; if so, it is probably the power amp.

    Does the preamp have a headphone jack? if so, you can test the levels of its outputs that way (i.e., independent of the power amp) -- or, of course, hook the suspect preamp to another power amp* and test it independent of the power amp you just had repaired.

    * You can, of course, hook the preamp's output to any line level input of any component (e.g., a receiver or integrated amp, even a boombox with "AUX" inputs!) to test it. Just be cautious with the volume control levels while testing.
  • mhardy6647mhardy6647 Posts: 20,982
    IF the problem seems to be "upstream" of the (power amp + preamp); try another pair of cables between the CDP and the preamp and test again.
  • pglbookpglbook Posts: 1,518
    Thanks. I just switched the CD player from CD jack on the back of the pre to the Direct jack on the back of the pre and the same problem: one speaker is about half volume of the other. I will switch cables now. I will also play a record to see if the same problem persists while playing the tt. If so, chances are we can rule out it being the CD player connection. The other thing is that the balance control knob on the pre does not seem to be working right. If I turn it all the way to one side (I forget if it was right or left), sound comes out of both speakers but , when I turn it all the way to the other side, there is no sound from either speaker. If it is in the middle of course there is sound from both speakers.
  • pglbookpglbook Posts: 1,518
    I just played the tt and the problem of low sound on one speaker was still there unfortunately.
  • mhardy6647mhardy6647 Posts: 20,982
    Sounds like the balance control pot (potentiometer) may be dirty (oxidized).
  • pglbookpglbook Posts: 1,518
    edited February 9
    mhardy6647 wrote: »
    Sounds like the balance control pot (potentiometer) may be dirty (oxidized).

    Thanks. There is no scratchy sound when I turn the balance control; just that, if turned all the way to one sound, no sound from speakers; and if turned all way to other side there is sound from both speakers. Balance control is definitely not working right but I do not think that would cause low volume in one speaker. And sound issue changed speakers when I switched speaker cables on back of amp so I am thinking that that channel is bad in amp. But of course I do not know anything about electronices so it is merely a guess, ha. Looks like another trip to the repair shop.
  • mhardy6647mhardy6647 Posts: 20,982
    Oh -- did you swap the outputs (L and R) channel from the preamp to the inputs of the power amp?

    Connect L out from the preamp to R in of the power amp (and vice versa). If the problem swaps from one speaker to the other; the issue's in the preamp; if it doesn't, it's the power amp.
  • mhardy6647mhardy6647 Posts: 20,982
    pglbook wrote: »
    ...And sound issue changed speakers when I switched speaker cables on back of amp so I am thinking that that channel is bad in amp. But of course I do not know anything about electronics so it is merely a guess, ha. Looks like another trip to the repair shop.

    Yes, but, if the input channel to the power amp is low, the ouput of that channel is going to be low; the power amp could be fine. Swapping the inputs to the amp (without swapping the outputs) should isolate the issue to the preamp or to the power amp.

    This isn't about electronics (yet); it's basic troubleshooting -- i.e., it's logic :)

  • pglbookpglbook Posts: 1,518
    edited February 9
    One last thing....the Parasound amp has 2 gain control knobs on the back of the amp...one for each speaker. If I turn the gain control knob for the right speaker (the speaker that sounds fine) all the way to the left (low gain/off position) and keep the gain control knob for the left speaker turned all the way to the right (full gain position), the result is no sound from either speaker. Not even any sound at all from the left speaker which has the gain control turned all the way to the right (highest position). I will do some more troubleshooting tomorrow but I am done for the night and need a beer..I guess I'll have to watch tv as I can't listen to music. Very frustrating...I was really looking forward to getting my equipment back in great shape and spending all night listening to music. But así es la vida. That's life. Thanks again for all of your help. It is much appreciated...and why this forum and the people on here are the best!
  • mhardy6647mhardy6647 Posts: 20,982
    edited February 9
    That's not good -- but, again, did you swap the output from the "RIGHT" side of the preamp to the "LEFT" input of the power amp, and then try your LEFT 'gain control knob' experiment? As best I can understand your descriptions, the issue could still be the signal from the preamp to the power amp.

    Also (and, gain, I may be misunderstanding) you seem to be describing two different observations; you said one channel played "low" in your first post, but you've also made some comments about one channel being "dead' (no sound output) -- so I am confused.

    Enjoy your beer! Sorry you have to watch TV; we avoid it as much as possible at my house (and I don't miss it a bit)! :blush:
  • mhardy6647mhardy6647 Posts: 20,982
    :p
    That could be a problem... :blush:
  • pglbookpglbook Posts: 1,518
    I talked to the repair tech today and he thinks it may be a loose balance control knob on the pre amp because (I am not sure if I mentioned this earlier) the outer balance control knob of the pre was loose and slipped off when I first tried to adjust the balance control. Could it be that simple? I have a phone call with the repair tech set for later tonight to try and troubleshoot the issue. I have my fingers crossed and am hoping it is a simple fix we can take care of tonight and I can play music again soon (and also avoid another 5 hour r/t drive to Syracuse).
  • mhardy6647mhardy6647 Posts: 20,982
    That would be weird but sure it could be that simple.
    Did you check the switch that @FTGV mentioned?
  • pglbookpglbook Posts: 1,518
    edited February 11
    mhardy6647 wrote: »
    That would be weird but sure it could be that simple.
    Did you check the switch that @FTGV mentioned?


    Thanks. I'll find out tonight if it is a simple solution or requires a return trip for further repairs. And, yes, the switch which FTGV mentioned was always in the correct stereo position so that was not it.
  • mhardy6647mhardy6647 Posts: 20,982
    well... unless the switch contacts are dirty :p It could happen.
    Did you ask the person who serviced it if he cleaned (all of) the controls? You might want to if tonight's amp whisperer troubleshooting session doesn't bear fruit.
  • motorhead43026motorhead43026 Posts: 3,105
    edited February 11
    Sounds like a goober worked on your equipment.
    2 channel: Anthem 225 Integrated amp; Parasound Ztuner; TechnicsTT SL1350; Vincent PHO-8 phono pre; Marantz CD6005 spinner; Polk SDA2BTL's; Cables ZU Mission IC's, SC and power cords, all into a PS Audio Dectet Power center.

    All TV's sound enhanced by Polk Magnfi Mini's.

    Other; S60'S, M10 series II, M7C's, Hafler XL600 amp, RB-980BX, Parasound HCA-1500 amp , P5 preamp, all in storage. All speakers have had crossover rebuilds, resulting in a small fortune invested in Sonicaps, and tweeter upgrades.

    Political memes posted as fact and accepted as fact, are sign language of the ignorant, for the ignorant

    tonyb said " but even socialists can do a good thing here and there

    Social media makes dumb people dumber and smart people dumb then dumber.
  • mhardy6647mhardy6647 Posts: 20,982
    Sounds like a goober worked on your equipment.

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    or...

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  • corticocortico Posts: 482
    I strongly recommend sending the amp to Parasound. Fantastic customer support, fair fees, and quick response.
    Parasound HC/A 2200II < PL/D 2000 < DA/C 1100HD < CD/C1500
    Cambridge Audio phono pre
    Pioneer PL530 turntable, Shure M97XE cartridge
    Belden ICs
    MIT T2 speaker cables
    Polk Audio LS70

    "If it measures good and sounds bad, it is bad"
  • pglbookpglbook Posts: 1,518
    cortico wrote: »
    I strongly recommend sending the amp to Parasound. Fantastic customer support, fair fees, and quick response.

    Thanks, cortico. However, since I already paid for the repairs, I am taking it back to the repair tech who did the initial work to diagnose and fix the ongoing problem. The repair is under warranty so he will either fix it or refund my money. Also, I do not know if the issue is with the amp or pre amp. Most likely it is the pre amp but that also needs to be determined.

  • mhardy6647mhardy6647 Posts: 20,982
    Not to get persnickety (it's not my amp and preamp!) but it still seems like you have a path to determine if it's the pre or the power amp. If nothing else, you could save some trouble and somone's expense in shipping just one rather than both.

    If you want them to do all the work, though, that's certainly your call.
  • pglbookpglbook Posts: 1,518
    mhardy6647 wrote: »
    Not to get persnickety (it's not my amp and preamp!) but it still seems like you have a path to determine if it's the pre or the power amp. If nothing else, you could save some trouble and somone's expense in shipping just one rather than both.

    If you want them to do all the work, though, that's certainly your call.

    Thanks, mhardy. I understand but I disconnected everything and put them away for now, pending further repair. I am driving the amp and pre amp back to the repair shop this weekend so no expense in shipping (just gas and time). Thanks again.
  • mhardy6647mhardy6647 Posts: 20,982
    cool enough; good luck -- sounds like they'll take care of you.
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